Freetrade offer commission-free trading via there app. They do have a range of ETFs/bonds/US stocks as well as UK and European shares.
They also offer Fractional shares for US-based stock so you can invest in a company at a level your happy with.
They currently are offering Free shares up to the value of £200 for new accounts via the link below
If your looking to expand your investment portfolio and are leaning towards cryptocurrencies Coinbase would be your best bet.
There currently offering £7.21 worth of bitcoin when you buy £72.1