Leveraged ETF's/products are often frowned upon. Personally I like and use them.
Consider a 2x stock ETF, what you buy of that the fund in effect borrows the same amount again in order to buy twice the amount of exposure. If you invest half the amount in that, deposit the other half in bonds, then that's comparable to the fund borrowing your bond amount to scale up exposure. Net outcome is that half in 2x, half in bonds will compare much the same to 100% 1x. Similar for 3x. A third in 3x, two-thirds in bonds compares to 100% 1x. A problem however is that leveraged holdings can deviate, what was originally half in 2x, half in bonds might drift to being 66/33 or 33/67. To mitigate that effect you have to rebalance a 2x around once/year back to 50/50 weightings, or for a 3x rebalance every 6 months back to 33/67 weightings.
Zvi Bodie takes that a step further and he buys into a 10x stock using 10%, holds bonds for the remainder 90%, and rebalances frequently (monthly). He gains that 10x exposure via LEAPS .. long dated Traded Options.
I quite like a third each in US stock, UK mid cap stock (which is small cap stock in US scale) and gold.
Here's a US version that is somewhat like that where for the first portfolio its using a combination of 3x and 2x holdings for the stock and gold assets, and that is compared to the straight 1x version (second portfolio).
In the UK ... Wisdom Tree's
3x gold,
3x US stock and
2x FT250 can be used to similar effect. That does however leave 64% in 'cash'. Which could be UK 1 year gilts or cash deposit ...etc.
Yes the expense ratios for those are high, but when you hold just around a third in total in those, two thirds in cash, that scales those costs down by two-thirds. Similarly £/$ currency conversions that might otherwise cost perhaps 1.5% as I believe iWeb apply, are again proportioned down to just a third, a more acceptable 0.5% cost. And they are all SIPP and ISA'able.
I do get quizzed when trading those (automated online basic "quiz"), to ensure I'm a sophisticated investor, which is a pain, especially when you're already holding them and looking to reduce/sell. i.e. the brokers are distancing themselves from the risks. But as I buy/hold them and trade infrequently that's not a great issue for me. And of course you get bombarded with the likes of them only being suitable for short term positions/trading, not viable long term holdings etc. However I've held leveraged ETF's on a buy and hold basis longer term (multiple years dating back to a year or two after 2MCL became available back in 2013). Periodically I do get SMS/text messages indicating that a 10% move has occurred, often in the middle of the night, which again is a bit of a pain. But then after a purge for a few days or so things go quiet again.
Holding around two thirds in cash is handy for cash flows. Whilst that should be earning interest to offset the leveraged funds borrowings, at recent low yields it doesn't matter that much if you 'borrow' from that. You can do other tricks to keep cash unchanged, such as scaling more into 3x, less into 2x or the other way around, so that overall cash, that might be tied up into perhaps a 1 year fixed term bond, can be left as-is.
There are other tricks as well, such as using long and short positions in around equal weightings that has the effect of migrating money from one account into another. Add to a SIPP for instance and you're credited with 20%, but can't touch that money until later in life. With long/short neutral positions however and the money can be migrated from SIPP to ISA/trading.
Some physical gold is nice, and personally I prefer Britannias for their lower spread between spot and coin prices. The spreads do drift around so buying when perhaps 3% or less is OK IMO. Only buy from reputable suppliers. Hattongardenmetals/coininvest tend to have acceptable spreads, but again that drifts. But for selling its OK to offer on the likes of thesilverforum.com where others might offer above spot to purchase your coins.
http://goldprice.eu5.net/ provides a quick indicator of different recent spreads across different suppliers. Best to check during business hours as out of hours the spreads tend to go extreme. One supplier that has recently come onto my radar is
https://www.gold.de/ but I have no experience with that outfit whatsoever. Their spreads however do seem very tight, around 2.5% between Britannia and spot when I looked last Tuesday afternoon when others were up at relatively high 4% type levels. So if you can buy for that and later another thesilverfourm member buys coins from you at perhaps spot+2% ...